In general, there are two types of intraocular lenses. One type replaces the eye's natural lens, usually to replace a cataractous lens. The other type is used to supplement an existing lens and functions as a permanent corrective lens. This type of lens (referred to as a phakic IOL) is implanted in the anterior or posterior chamber to correct refractive errors of the eye. In theory, the power for either type of IOL required for enmetropia (i.e., point focus on the retina from light originating at infinity) can be precisely calculated. The power of the implanted lens is selected based on pre-operative measurements of ocular length and corneal curvature to enable the patient to see without or with little vision correction. Unfortunately, due to errors in measurement, variable lens positioning or wound healing, most patients undergoing cataract surgery will not enjoy optimal vision without some form of vision correction following the surgery (Brandser et al., Acta Opthalmol Scand 75:162 165 (1997); Oshika et al., J Cataract Refract Surg 24:509 514 (1998). Because the power of present IOLs cannot be adjusted post-implantation, the patient typically must use additional corrective lenses such as eye glasses or contact lenses.
One potential solution to the foregoing problem is a light-adjustable intraocular lens whose refraction properties can be modified following insertion of the lens into a human eye. Such a lens is reported in U.S. Pat. No. 6,450,642, hereafter referred to as the Calhoun Patent. The light-adjustable lens is said to comprise (i) a first polymer matrix and (ii) a refraction modulating composition (RMC) that is capable of stimulus-induced polymerization. As stated, when a portion of the described lens is exposed to light of sufficient intensity, the RMC forms a second polymer matrix. The process is said to result in a light adjusted, power-modified lens.
As described in the Calhoun Patent, the first polymer matrix and the RMC are selected such that the components that comprise the RMC are capable of diffusion within the first polymer matrix. Put another way, a loose first polymer matrix will tend to be paired with larger RMC components and a tight first polymer matrix will tend to be paired with smaller RMC components. Upon exposure to an appropriate energy source (e.g., heat or light), the RMC typically forms a second polymer matrix in the exposed region of the optical element. After exposure, the RMC in the unexposed region will migrate into the exposed region over time. The amount of RMC migration into the exposed region is time dependent and may be precisely controlled. If enough time is permitted, the RMC components will re-equilibrate and redistribute throughout the lens material (i.e., the first polymer matrix, including the exposed region). When the region is re-exposed to the energy source, the RMC that has since migrated into the region polymerizes to further increase the formation of the second polymer matrix. This process (exposure followed by an appropriate time interval to allow for diffusion) may be repeated until the exposed region of the optical element has reached the desired property (e.g., power, refractive index, or shape). The entire optical element is then exposed to an energy source to “lock-in” the desired lens property by polymerizing the remaining RMC in the lens material. Overall, the power of the lens is changed by a shape change caused by the migrating of the RMC and subsequent polymerization(s).
U.S. Pat. No. 7,105,110 describes a method and instrument to irradiate a light adjustable lens with an appropriate amount of radiation in an appropriate pattern. The method is said to include aligning a source of the modifying radiation so as to impinge the radiation onto the lens in a pattern, and controlling the quantity of the impinging radiation. The quantity of the impinging radiation is controlled by controlling the intensity and duration of the irradiation.
There exists an ongoing need for new materials and processes to improve a patient's vision following cataract surgery. In particular, there is a need for an IOL material whose refractive power can be modified by a change in the refractive index of the lens material post-operative implantation.